I think it could work, depending on the rabbits. It used to be more common for females to be unspayed. It certainly makes things easier and more likely to work, but there are cases where it works out, especially when the female is old enough. If the male was calm around other bunnies and she was as well, then it could be successful. Would the humane society let you bring her in for a speed date? Or potentially do a foster-to-adopt situation with the male?
I think in this case especially you would just want to have a back up plan in case the bond doesn’t work out (or appears to work, but then fails down the line). Would you be ready to keep both buns separately or rehome one if that was the case?
If she is in good health, I don’t think she is too old to be bonded, but you would just want to keep a close eye on her health during the process. Bonding in itself is stressful and can be hard on bunnies, so with seniors you really need to go at their pace and not force anything.
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.